There are devices known in the related art that control a pump displacement by driving a proportional electromagnetic valve based upon a displacement control signal corresponding to the extent to which an operation lever is operated, output to the proportional electromagnetic valve (see, for instance, Patent Reference Literature #1). In order to account for any inconsistency in the control characteristics that may exist among individual proportional electromagnetic valves, such a control device controls the proportional electromagnetic valve based upon a correction expression to be used for pump displacement correction determined in correspondence to the deviation of the actual pump displacement relative to a target pump displacement.    Patent Reference Literature 1: Japanese Laid Open Patent Publication No. H8-302755